Alex McLeish says he can "understand" Brendan Rodgers' desire to bring in more quality signings at Celtic.
Last week, Rodgers refused to answer if the Celtic board matched his ambitions.
So far this window Celtic have brought in Odsonne Edouard, Scott Bain and Emilio Izaguirre, with target John McGinn moving to Aston Villa.
"Brendan sets high standards so you can understand where he is coming from," Scotland manager McLeish told BBC Scotland.
"In terms of sympathising, it's just part of the challenge."
McLeish spent five years as Rangers manager where he had to juggle competing domestically and on the European stage.
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Rodgers is bidding to take Celtic into the Champions League group stage for the third season in a row, with his side tied 1-1 with AEK Athens before Tuesday's third qualifying round second leg in Greece.
"Brendan has taken on fantastic challenges in the past and come through them," he said.
"He's shown how good he is as a manager.
"Steven Gerrard has now taken a step into management [at Rangers]. There's challenges ahead and you've got to make the most of it.
"You've got to remain positive and you have to have rhinoceros skin."
McLeish is preparing for a friendly with Belgium at Hampden on 7 September before Scotland commence their Nations League campaign at home to Albania three days later.
And he admits it has been a difficult summer of watching the World Cup from afar waiting for Scotland to return to action.
"Agony. Every time there's a major tournament as a Scotland supporter then it's really gut-wrenching that we're not there," he said.
"There's no doubt the Tartan Army tuning in to watch the World Cup as well, and everyone else from the players to the manager, seeing that we're not there is something we really must aspire to big time.
"We still have to prove it. It's easy for me to say we're not far away.
"The perception is Scotland will fail again and we won't do it. We have to believe in ourselves and if we can get the fans coming in their hoards again we can do something for them on the field, then we have to follow these small countries like Iceland.
"It's phenomenal achievements and that's what Scotland has to aspire to."